#define _BSD_SOURCE

#include <ncurses.h>
#include <unistd.h>

#define MAX_X 100.0
#define MAX_Y 100.0
#define MAX_R 24
#define MAX_C 80

void xy2rc(float x, float y, int *r, int *c) {
  int mrow, mcol;
  getmaxyx(stdscr, mrow, mcol);

  *c = (x / MAX_X) * mcol;
  *r = mrow - ((y / MAX_Y) * mrow);
}

float lerp(float from, float to, float t) {
  return from + t * (to - from);
}

float ball_x = 0.0;
float ball_y = 0.0;
float dir_x = +2.0;
float dir_y = +1.0;

float pad_l = 0.0;
float pad_r = 0.0;

void paint_ball() {
  int r, c;
  xy2rc(ball_x, ball_y, &r, &c);
  mvaddch(r, c, ACS_DIAMOND);
}

void paint_paddles() {
  int r, c;
  xy2rc(0, pad_l, &r, &c);
  mvaddch(r, c, ACS_VLINE);

  xy2rc(MAX_X, pad_r, &r, &c);
  c--;
  mvaddch(r, c, ACS_VLINE);
}

void paint() {
  clear();
  paint_paddles();
  paint_ball();

  refresh();
}

int main() {
  initscr();                    /* Start curses mode */
  curs_set(0);                  /* Disable cursor */

  while (true) {
    ball_x += dir_x;
    ball_y += dir_y;

    if (ball_x > MAX_X || ball_x < 0) {
      dir_x = -dir_x;
    }
    if (ball_y > MAX_Y || ball_y < 0) {
      dir_y = -dir_y;
    }

    /* Awesome artificial intelligence working here. */
    if (ball_x < 0.25f * MAX_X) {
      pad_l = lerp(pad_l, ball_y, 0.3);
    }
    if (ball_x > 0.75f * MAX_X) {
      pad_r = lerp(pad_r, ball_y, 0.3);
    }

    paint();
    usleep(50000);
  }

  getch();                      /* Wait for user input */
  endwin();                     /* End curses mode */
}